Since polyolefin such as polypropylene, high-density polyethylene, straight chain low-density polyethylene or the like is excellent in mechanical properties, chemical resistance or the like and is extremely useful in respect of a balance with economy, it has been used in a variety of molding fields. However, the polyolefin has a small melt tension and low crystallization temperature. For this reason, molding properties such as hollow molding, foaming molding, extruding molding and the like are poor and the high-speed productivity of a molded product has limitations in various molding methods other than the above.
A method for causing polypropylene to react with organic peroxide and a crosslinking auxiliary agent in the molten state (see, for example, Japanese Patent Application Publication (Tokko Sho) Nos. 59-93711 and 61-152754 and the like), a method for causing low decomposition temperature peroxide to react with semi-crystalline polypropylene in the absence of oxygen to produce polypropylene that has a free end long chain branch and does not contain gel (Japanese Patent Application Publication (Tokko Hei) No. 2-298536) and the like have been disclosed as a method for increasing the melt tension and crystallization temperature of polypropylene.
In addition, a method in which semi-crystalline polypropylene is irradiated with electron rays to produce polypropylene that has a free end long chain branch and does not contain gel has been considered (Japanese Patent Application Publication (Tokko Hei) No. 2-298536).
A composition in which polyethylene or polypropylene having different limiting viscosity or molecular weight is blended and a method for producing such a composition by multistep polymerization has been proposed as another method for improving melt viscoelasticity such as melt tension or the like.
There have been disclosed a method for adding 2 to 30 parts by weight of superhigh molecular weight polypropylene to 100 parts by weight of ordinary polypropylene and extruding a product at a temperature that is a melting point or higher and not higher than 210.degree. C. (Japanese Patent Application Publication (Tokko Sho) No. 61-28694), an extrusion sheet made of polypropylene that is obtained by a multistep polymerizing method and contains two components having a limiting viscosity ratio between them of 2 or more and different molecular weights each other (Japanese Patent Application Publication (Tokko Hei) No. 1-12770), a method for producing a polyethylene composition that contains 1 to 10 weight % of polyethylene having high viscosity-average molecular weight and that comprises three kinds of polyethylene having different viscosity-average molecular weights each other by a melting and kneading method or a multistep polymerizing method (Japanese Patent Application Publication (Tokko Sho) No. 62-61057), a method of polymerizing not less than 0.05 weight % and less than 1 weight % of superhigh molecular weight polyethylene having a limiting viscosity of 20 dl/g or more by a multistep polymerizing method by using a highly active titanium-vanadium solid catalyst component (Japanese Patent Application Publication (Tokko Hei) No. 5-79683), a method for polymerizing 0.1 to 5 weight % of superhigh molecular weight polyethylene having a limiting viscosity of 15 dl/g or more by using a highly active titanium catalyst component that has preliminarily been polymerized with 1-butene or 4-methyl-1-pentene by a multistep polymerizing method using a polymerization reactor having a special arrangement (Japanese Patent Application Publication (Tokko Hei) No. 7-8890) and the like.
Furthermore, there have been disclosed a method for producing polypropylene having a high melt tension in which propylene is polymerized by using a preliminary polymerization catalyst that is prepared by preliminarily polymerizing ethylene and a polyene compound on a supported titanium-containing catalyst solid component and an organic aluminum compound catalyst component (Japanese Patent Application Publication (Tokkai Hei) No. 5-222122), and a method for producing an ethylene.multidot..alpha.-olefin copolymer having high melt tension by using an ethylene-containing preliminary polymerization catalyst that contains polyethylene having a limiting viscosity of 20 dl/g or more that is obtained by preliminarily polymerizing only ethylene by using the same catalyst component (Japanese Patent Application Publication (Tokko Hei) No. 4-55410).
As mentioned above, according to various compositions and producing methods proposed in the prior art, the melt tension can be enhanced to some extent. However, some problems, for example, residual odor, crystallization temperature, thermal stability, irradiation rate of electron rays and the like remain to be unsolved.
The process for producing high molecular weight polyolefin should be modified for the following reasons. More specifically, it is difficult closely to control the amount of olefin (co)polymerization in order to produce a small amount of polyolefin having a high molecular weight in the multistep polymerizing method that is to be incorporated into the ordinary olefin (co)polymerizing step for the main polymerization; and in addition, it is necessary to lower the polymerization temperature so as to produce polyolefin having a sufficiently high molecular weight. Furthermore, the productivity of the final polyolefin composition is lowered.
In the method for preliminarily polymerizing the polyene compound, it is necessary to prepare the polyene compound separately. In the method for preliminarily polymerizing polyethylene, the dispersion property of the preliminarily polymerized polyethylene to the polyolefin composition that is to be finally obtained is ununiform. Consequently, further improvement should be required in respect of the stability of the polyolefin composition.
Furthermore, as a method for improving the rigidity and heat resistance or the like of propylene polymer, a method for irradiating a molding including propylene polymer, which is formed by the copolymerization of propylene and alkenylsilane, with ionizing radiation so as to obtain a propylene polymer molding that is excellent in heat resistance and rigidity (Japanese Patent Application Publication (Tokko Hei) No. 3-50239).
As mentioned above, in the prior art, the polyolefin such as polypropylene polymer or the like has problems to be solved. Examples of problems include: the insufficient improvement in strength such as melt tension or the like at the time of melting and in crystallization temperature; the insufficient improvement in heat resistance, rigidity and the like; insufficient in irradiation efficiency of ionizing radiation; a problem in terms of odor or thermal stability; a problem in which a comonomer other than olefin is required and the like. Furthermore, when such a polymer is produced, the productivity is required to be improved.
It is therefore an object of the present invention to provide a modified olefin (co)polymer composition having a high melt tension and a high crystallization temperature, which is suitable for hollow molding, foaming molding and extruding molding and also capable of exhibiting a high speed productivity in the other various molding methods as well as the above; a molded modified olefin (co)polymer composition that is excellent in physical properties such as heat resistance and rigidity and the like; and a method for producing the modified olefin (co)polymer composition and the molded modified olefin (co)polymer composition.